Treatment process for hypereutectic cast irons



product.

Patented Feb. 19, 1952 UNITED STAT TREATMENT PROCESS FOR HYPEREU- TECTICCAST IRONS Eugene Eyt,

Pamicrs, Ariege, and Lonce Reygagne, Decazeville, Aveyron, France,assignors to Societe Anonyme .de Commentry, Fourchambault & Decazeville,Paris, France, a

company of France No Drawing. Application Fe'bruary'17f1950, Serial No.144,845. In France March 30, 1949 2 Claims.

In conventional industrial practice, and in the case of mostblast-furnaces, the range of compositions of raw cast-irons which may beproduced with acceptable technical and economical conditions, is quitenarrow. However, these cast-irons are not always the most appropriate asregards the requirements of consumers. Moreover, it has seldom beencontemplated to improve or alter the composition of blast-furnace rawcast-iron considered as a starting The present invention particularlyconcerns hypereutectic cast-irons, for instance those which may beobtained according to the U. S. patent application Serial No. 111,905filed August 23, 1949. It relates to a process enabling to alter thecomposition and properties of these cast-irons by lowering their carboncontent and if needs be their silicon content.

It further concerns cast-irons obtained there- Although in the presentspecification, only blast-furnaces and blast-furnace cast-irons will bereferred to for the sake of simplification, the invention concernscast-iron of any kind, of any origin and of any preparation, whether itbe of first fusion produced in any apparatus or of second fusion, 1. e.resmelted in any apparatus: e. g. cupola, electric furnace,reverberatory furnace, etc.

It is known that the solidification point of hypereutegtic cast-irondecreases as its carbon content decreases, contrarily to the phenomenonoccuring in the case of hypoeutectic castiron whose solidification pointincreases when the carbon content decreases. Thus this point drops fromabout 1800 C. for a carbon content of 6.67% (cementite FesC) to 1135 C.for the eutectic content which is 4.30% in the iron-carbon system; asimilar variation but of different absolute value, occurs in the case ofcast-irons containing other constituents. On the contrary, thesolidification point increases when the carbon content drops below theeutectic value.

According to the invention, the calories are used which are madeavailable owing to the drop in solidification point corresponding to thecorrection to be applied to the carbon content of hypereutecticcast-irons discharged by a blastfurnace, for melting iron or steel in arelatively divided state (light scrap-iron, steel turnings, etc. whetherpreviously heated or not, whether oxidized or not, for the purpose oflowering by dilution and/or by oxidation, the initial carbon content.The addition of metallie or oxidized iron must be proportionedaccordingto the desired reduced carbon content which may be either greater orlower than the eutectic content; obviously, it is necessary to take intoaccount the rise in the solidification point. of cast-iron whichaccompanies the'decrease in the carbon content below that eutecticcontent, and as a rule to proportion the addition of. iron so that thetemperature of cast-iron, after addition, remains high enough above itssolidification point, this temperature margin being determined accordingto the subsequent treatment to which cast-iron is to be subjected.

This proportioned addition of iron or steel, oxidized or not, which maybe carried out in the ladle into which the hypereutectic cast-iron ispoured, causes not only the carbon content to be adjusted, but also toact in a favorable way on the structure by homogenizing the thickness ofgraphite flakes and their distribution. This homogenization results inan improvement of the mechanical properties of cast-iron. Moreover, theamount of coke per unit weight of cast-iron eventually obtained isdecreased by the increase in production due to the conversion of addediron or steel to cast-iron, owing to the calories recovered withincast-iron.

In order to decrease the silicon content, the excess silicon may beburnt by oxygen contained in iron oxide which is-obt'ained at thesurface of the iron or steel in a divided state added to cast-iron asdescribed above, by previously heating these substances by means of anoxidizing flame. It is also possible to replace iron or steel in thedivided state and superficially oxidized as stated, by iron oxides suchas scale, granular or powdery ores, etc.

A fraction of the oxygen content of the oxides burns a part of thecarbon content of cast-iron into carbon monoxide and carbon dioxide;another fraction reacting with silicon, evolves an amount of heatgreater than that required by the decomposition of the oxides. Thesecalories together with the heat due to the difference between the actualtemperature of cast-iron and that necesary for its pouring, areavailable for melting ferrous metallic substances after reduction of theoxides which they possibly contain. Lastly, a portion of the addition isscorified together with the oxidation products of cast-iron (MnO, S102,etc.). By a convenient predetermined addition of the mixture of iron inthe divided state and of granular or powdery iron oxide, a decrease inthe carbon and silicon contents is achieved, and a slag is formed whoseproperties determine the form of graphitization 0f cast-iron.

According to the cases, the proportions between the additions of iron orsteel and of iron oxides may vary within very wide limits. Theseadditions may be eifected either in a sprue, or in a convenient vessel,whether fixed or movable,

heated or non-heated, and into which cast-iron is poured. They may beeffected in a continuous way in the sprue or in the vessel, or by massadditions once or several times.

It is also possible to lower the silicon and carbon contents whileobtaining a rise in temperature of the metallic bath, "by blowing in apredetermined amount of oxygen.

What we claim is:

1. In a treatment process for lowering the carbon content and thesilicon content or raw hypereutectic iron, the pouring of saidhypereutectic iron from a blast-furnace; the addition to said liquidhypereutectic iron of a mixture of low carbon iron and iron oxide in arelatively divided state; and the melting of said mixture by the heatwhich is contained in excess in said hypereuteotic iron owing to thelowering of its solidification point when its carbon content decreases.

2. In a treatment process for lowering both the carbon content 'ahd 'thesilicon content of raw hypereutectic iron, the steps which comprisetaking low-carbon fironin'a relatively 'dividecl state, oxidizingsuperficially and heating said low-carbon iron by subjecting it to theaction of an oxidizing flame, pouring molten hypereutectic iron from afurnace and adding to it when in liquid state said partially oxidizedand heated low-carbon iron only in an amount adapted to the melting ofsaid low-carbon iron by the heat contained in excess in thehypereuteotic iron owing to the lowering of the solidification point ofthe latter when its carbon content decreases.

EUGENE EYT.

LEONCE REYGAGNE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 77,469 Ellershausen May 5, 186890,926 Chubb June 8, 1869 173,159 Carpenter Feb. '8, 1876 FOREIGNPATENTS Number Country Date 3,631 Great Britain of 1868 111,522Australia Sept. 26,1940

OTHER REFERENCES Cast Iron, page 31, edited by Hatfield.

Published in 1912 by Charles Griffin and Co., London, England.

1. IN A TREATMENT PROCESS FOR LOWERING THE CARBON CONTENT AND THESILICON CONTENT OF RAW HYPEREUTECTIC IRON, THE POURING OF SAIDHYPEREUTECTIC IRON FROM A BLAST-FURNACE; THE ADDITION TO SAID LIQUIDHYPEREUTECTIC IRON OF A MIXTURE OF LOW CARBON IRON AND IRON OXIDE IN ARELATIVELY DIVIDED STATE; AND THE MELTING OF SAID MIXTURE BY THE HEATWHICH IS CONTAINED IN EXCESS IN SAID HYPEREUTECTIC IRON OWING TO THELOWERING OF ITS SOLIDIFICATION POINT WHEN ITS CARBON CONTENT DECREASES.